Stretchable electronics have emerged as a new type of devices having better mechanical compliance compared to their rigid or flexible counterparts. They may be able to tolerate demanding mechanical deformations such as stretching, flexing, twisting, folding, or conformably wrapping, which make them suitable for electronic applications requiring rigorous mechanical conditions that cannot be addressed by the use of conventional electronic devices. Such stretchable electronic devices may be also referred to as “soft” electronics.
An interesting type of soft electronics which seems to have spurred significant interest is the stretchable electroluminescent (EL) device. The EL device may become an essential technology in future lighting and display applications. The soft physical form or stretchable property may render such devices to be suitable for unprecedented applications, such as biomedical related applications that involve implantable devices on curvilinear tissue surfaces, three-dimensional displays that render contents physically, or visual systems which provide users with tactile interaction besides visual information etc. Particularly, stretchable conductors may play an important role in the construction of deformable EL devices that may be used for such applications.
In order to fabricate stretchable electrodes, two different strategies have been developed. The first strategy focuses on stretchable structures while the second focuses on stretchable materials. However, due to intractable material challenges faced when developing electronic conductors, efforts have been mainly geared towards developing conductors with stretchable structures for deformable EL devices. For example, thin metal films have been conventionally patterned into stretchable structures for use as electrical interconnects to assemble rigid light-emitting elements on elastic substrates. Conventional technologies may also be combined with this approach to derive stretchable electronics. However, this may be impeded by challenges such as a need for large-scale and cost-effective techniques to be developed so as to manipulate the stretchable structures, and a requirement to assemble components with significant mechanical incompatibilities to form durable deformable devices. Furthermore, since the metal films may be opaque, the developed electrodes may be unsuitable for use as stretchable EL devices which require good transmittance for efficient light extraction.
Recently, carbon nanotubes (CNTs) and silver nanowires (AgNWs) have been used as highly conductive fillers in polymer matrix for forming transparent and stretchable electrodes with their percolating network structure. When combined with stretchable emissive layers, the transparent and stretchable electrodes may be used to form fully stretchable EL devices. Although stretchable devices at moderate strains may be achieved in this manner, it remains challenging to improve the stretching strains of these thin and transparent nanowire networks beyond 100% due to the damage on the network structure when subjected to large mechanical deformations. Due to this stretchability limitation in conventional transparent electronic conductors, alternating-current electroluminescent (ACEL) devices derived through the above means may only sustain a strain of 100% before deteriorating.